This invention relates generally to semiconductor integrated circuit packages and more particularly, it relates to an improved ball grid array (BGA) package.
As is generally known in the art of integrated circuit packaging, an integrated-circuit die is typically attached to a die-attach pad, which is located at the central region of a conventional lead frame. In particular, the lead frames are manufactured in long strips of many individual units. These long strips can be made long enough in order to accommodate any number of lead frames. Further, the lead frames may be formed with carrier rails and guide holes for positioning the same during manufacturing. Each lead frame consists of a plurality of internal and external leads, tie bars, and the die-attach pad. The die-attach pad provides a surface on which the die may be mounted. The lead frames vary in their sizes dependent upon the size of the die and the number of connections required to be made to the die.
Conventional lead frame plating processes will provide lead frames that have clean, non-reactive finishes. During packaging, the die is mounted to the die-attach pad. Bonding pads are provided on the surface of the die and are connected to the internal leads of the lead frame by bonding wires in accordance with known techniques. In order to improve the thermal performance of a package, a thermally-conductive electrically-insulated substrate formed of, for example, a glass epoxy material or the like is either attached to the die-attach pad via a layer of adhesive or is used to replace the same. In the case where the substrate replaces the die-attach pad of the conventional lead frame, the die is mounted directly to the substrate. The substrate may be in the form of a printed circuit board having conductive traces disposed on its top surface. Bonding wires are used to join the pads on the die to the conductive traces. Then, the die-attached pad/substrate, die leads, and associated connections are encapsulated in an encapsulating material such as a plastic molding compound. A ball grid array (BGA) package provides an array of solder balls on its lower surface. After encapsulation of the die and the lead frame with the plastic molding material, the solder balls are attached and the packages are singulated.
One of the most critical steps in the BGA process is the molding step. What is needed is a low-stress molding compound which can provide good adhesion to the substrate. Delamination of the encapsulating material from the substrate is a common problem encountered in BGA integrated circuit packages. There are a number of reasons why this problem may occur, such as improper curing of the encapsulating material, surface contamination of the substrate, or warpage between the encapsulating material and the substrate. Further, another reason for encapsulating material failure is because of the thermal mismatch between dissimilar materials of the substrate and the encapsulating material.
A BGA integrated circuit package utilizing a substrate also has the disadvantage of being more expensive because of the additional cost of the substrate itself and the additional cost of assembling a package with a substrate. Consequently, it is desirable to provide a BGA package which has a relatively simple construction and which is inexpensive to manufacture.